Substrate processing apparatus and substrate processing method

ABSTRACT

A substrate processing apparatus flows a propagation liquid for propagating ultrasonic vibrations, and controls the flow rate thereof. The ultrasonic vibrations are scattered by the flow of the propagation liquid, so that a concentrated impact of the ultrasonic vibrations given on a substrate is relieved. The substrate processing apparatus can increase the output power of ultrasonic vibrations by controlling the flow rate of the propagation liquid while preventing a fine pattern formed on the substrate from stripping or falling down.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate processing apparatus and a substrate processing method for performing predetermined processing on substrates, such as semiconductor substrates and glass substrates for liquid crystal displays or for photomasks, by immersing the substrates in a processing liquid.

2. Description of the Background Art

In the substrate manufacturing process, there are conventionally known substrate processing apparatuses for performing predetermined processing on substrates by immersing the substrates in a processing liquid retained in a processing bath. Particularly in recent years, substrate processing apparatuses have become commercially practical in which ultrasonic vibrations are applied to a processing liquid in a processing bath to perform substrate processing using the physical action of the ultrasonic vibrations.

Conventional substrate processing apparatuses using ultrasonic vibrations propagate ultrasonic vibrations generated by an ultrasonic vibrator to a processing bath through a propagation liquid such as deionized water. In the processing bath, ultrasonic vibrations propagate to substrates immersed in a processing liquid, so that predetermined processing is performed on the substrates. In this manner, subjecting the substrates to the action of ultrasonic vibrations allows particles adhered to the substrate surface to be effectively separated from the substrate surface in a cleaning process of the substrates, for example. This allows effective removal of particles adhered to the substrate surface.

In the above-described conventional substrate processing apparatuses, however, increasing the output power of ultrasonic vibrations may cause a fine pattern on substrates to strip or fall down due to the impact of the ultrasonic vibrations. For instance, part of a pattern 90 formed on the surface of a substrate W shown in the upper portion of FIG. 10 may strip and disappear as shown in the lower portion of FIG. 10. Particularly in recent years, the aspect ratio (b/a between pattern depth b and width a) of a pattern formed on substrates tends to increase, causing the pattern to be more likely to strip or fall down. Under such circumstances, the output power of ultrasonic vibrations cannot be increased sufficiently during substrate processing, which makes it difficult to cause a desired physical action to be exerted by ultrasonic vibrations.

SUMMARY OF THE INVENTION

The present invention is directed to a substrate processing apparatus for immersing a substrate in a processing liquid to process the substrate.

According to the invention, the substrate processing apparatus comprises: a processing bath retaining the processing liquid; a holder holding the substrate in the processing bath; an ultrasonic vibration generator generating ultrasonic vibrations; a propagation bath retaining a propagation liquid for propagating the ultrasonic vibrations generated by the ultrasonic vibration generator to the processing bath; a liquid flow generator generating a flow of the propagation liquid in the propagation bath; and a flow rate controller controlling a flow rate of the propagation liquid generated by the liquid flow generator.

The ultrasonic vibrations are scattered by the flow of the propagation liquid. Therefore, a concentrated impact of the ultrasonic vibrations given on the substrate is relieved. The substrate processing apparatus can increase the output power of ultrasonic vibrations by controlling the flow rate of the propagation liquid while preventing a fine pattern formed on the substrate from stripping or falling down.

Preferably, the flow of the propagation liquid is generated in a direction that crosses travel of the ultrasonic vibrations in the propagation bath.

The ultrasonic vibrations are scattered effectively. Therefore, a concentrated impact of the ultrasonic vibrations given on the substrate is relieved.

Preferably, the ultrasonic vibration generator is capable of controlling an output power of the ultrasonic vibrations. The substrate processing apparatus further comprises a controller controlling the ultrasonic vibration generator and the flow rate controller in synchronization with each other.

The substrate processing apparatus can automatically control the flow rate of the propagation liquid on the basis of variations in output power of ultrasonic vibrations.

Preferably, the liquid flow generator includes a supplier supplying the propagation liquid into the propagation bath and a discharger discharging the propagation liquid from the propagation bath.

The substrate processing apparatus can easily generate the flow of the propagation liquid in the propagation bath.

The present invention is also directed to a substrate processing method of processing a substrate.

It is therefore an object of the present invention to provide a substrate processing apparatus and a substrate processing method capable of increasing the output power of ultrasonic vibrations while preventing a fine pattern formed on a substrate from stripping or falling down.

These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a substrate processing apparatus according to the present invention taken along a plane parallel to substrates;

FIG. 2 is a vertical sectional view of the substrate processing apparatus taken along a plane perpendicular to substrates;

FIG. 3 is a diagram illustrating the flow of propagation liquid and the direction of travel of ultrasonic vibrations;

FIG. 4 is a flow chart illustrating the flow of cleaning process performed by the substrate processing apparatus;

FIG. 5 is a diagram illustrating an exemplary correlation between the output power of ultrasonic vibrations and the flow rate of propagation liquid;

FIGS. 6 and 7 are diagrams each illustrating experimental results of the relationship between the output power of ultrasonic vibrations and the number of defects occurred per substrate with a propagation liquid kept still;

FIG. 8 is a diagram illustrating experimental results of the relationship between the flow rate of propagation liquid and the sound pressure of ultrasonic vibrations propagated in a processing liquid;

FIG. 9 is a diagram illustrating experimental results of the relationship between the output power of ultrasonic vibrations and the number of defects occurred per substrate with a flow of propagation liquid generated; and

FIG. 10 is a sectional view of an electric pattern formed on substrate surface and an example of defect.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, a preferred embodiment of the present invention will be described with reference to the drawings.

1. Configuration of Substrate Processing Apparatus FIG. 1 is a vertical sectional view of a substrate processing apparatus 1 according to the present invention taken along a plane parallel to substrates W. FIG. 1 also shows piping and the structure of a control system. FIG. 2 is a vertical sectional view of the substrate processing apparatus 1 taken along a plane perpendicular to the substrates W. The substrate processing apparatus 1 is an apparatus for cleaning a plurality of substrates W, and is mainly provided with a processing bath 10, a lifter 20, a propagation bath 30, an ultrasonic vibrator 40 and a controller 50.

The processing bath 10 is a reservoir for retaining a processing liquid. The substrate processing apparatus 1 immerses the substrates W in the processing liquid retained in the processing bath 10, to thereby perform cleaning on the substrates W. Deionized water is used for the processing liquid, for example, however, a liquid chemical such as SC-1 may be adopted instead. The processing bath 10 has a pair of discharge ports 11 at the bottom. The discharge ports 11 are connected to a processing liquid supply source 13 via a pipe 12, and a valve 14 is interposed in the pipe 12. Accordingly, opening the valve 14 causes the processing liquid to be discharged from the processing liquid supply source 13 into the processing bath 10 via the pipe 12 and discharge ports 11.

The upper surface of the processing bath 10 is open, and the top edge of its outer surface is provided with an external bath 15. A pipe 16 has one side connected to the external bath 15, and the other side connected to a drainage line. Accordingly, the processing liquid discharged from the discharge ports 11 flows upward from the bottom within the processing bath 10 and then overflows from the upper opening to the external bath 15. The processing liquid overflown to the external bath 15 is discharged to the drainage line via the pipe 16.

The lifter 20 has three holding bars 23 extending in a horizontal direction between a lifter head 21 and a holding plate 22. The holding bars 23 each have a plurality of holding grooves (not shown) engraved thereon. A plurality of substrates W are held in upright positions on the holding grooves. The lifter 20 is connected to a lifter drive 24 having a servo motor, a timing belt, and the like. Operating the lifter drive 24 moves the lifter 20 up and down, so that the plurality of substrates W move between their immersed positions in the processing bath 10 (the position shown in FIGS. 1 and 2) and their raised positions above the processing bath 10.

The propagation bath 30 is a reservoir for retaining a propagation liquid (propagation water) serving as a propagation medium for ultrasonic vibrations. As the propagation liquid, deionized water or deaerated deionized water is adopted, for example. The propagation bath 30 is disposed under the processing bath 10, and the processing bath 10 has its bottom immersed in the propagation liquid retained in the propagation bath 30.

The propagation bath 30 is connected to a propagation liquid supply source 32 via a pipe 31, and a flow meter 33 and a valve 34 are interposed in the pipe 31. Accordingly, opening the valve 34 supplies the propagation liquid from the propagation liquid supply source 32 into the propagation bath 30 via the pipe 31. The valve 34 is a variable flow valve whose degree of opening is controllable. Accordingly, controlling the degree of opening of the valve 34 allows control of the flow rate of the propagation liquid supplied into the propagation bath 30. The flow rate of the propagation liquid in the pipe 31 is measured by the flow meter 33. The propagation bath 30 is connected to the drainage line via a pipe 35. Accordingly, the propagation liquid retained in the propagation bath 30 more than a predetermined amount is discharged to the drainage line via the pipe 35.

The ultrasonic vibrator 40 is provided at the back of the bottom surface of the propagation bath 30. Operating the ultrasonic vibrator 40 generates ultrasonic vibrations. The generated ultrasonic vibrations cause vibration of the bottom of the propagation bath 30, the propagation liquid in the propagation bath 30, the bottom of the processing bath 10, and processing liquid in the processing bath 10 in sequence, and then reach the substrates W immersed in the processing liquid. The output power of ultrasonic vibrations generated by the ultrasonic vibrator 40 is controllable by the control of the controller 50 which will be described later.

FIG. 3 is a diagram illustrating the flow of propagation liquid in the propagation bath 30 and the direction of travel of ultrasonic vibrations in the propagation liquid. The ultrasonic vibrations generated by the ultrasonic vibrator 40 travel upward in the propagation liquid from the bottom of the propagation bath 30 toward the bottom of the processing bath 10 (along arrows indicated by broken lines in FIG. 3). The pipe 31 for supplying the propagation liquid and the pipe 35 for discharging the propagation liquid are provided on the opposite sides to each other with the processing bath 10 interposed therebetween. Accordingly, supplying the propagation liquid via the pipe 31 while discharging the propagation liquid via the pipe 35 generates a flow of propagation liquid in the propagation bath 30 along the bottom of the processing bath 10 (along hollow arrows in FIG. 3). In short, the flow of the propagation liquid is generated so as to cross the travel of ultrasonic vibrations.

Referring again to FIG. 1, the controller 50 is constructed from a computer including a CPU and a memory, for example. The controller 50 is electrically connected to the flow meter 33, and receives measurements from the flow meter 33. The controller 50 is further electrically connected to the aforementioned lifter drive 24, ultrasonic vibrator 40 and valves 14 and 34, for controlling the operations of these components on the basis of a predetermined program. The controller 50 controls the ultrasonic vibrator 40, to thereby control the output power of ultrasonic vibrations generated by the ultrasonic vibrator 40. Further, the controller 50 controls the degree of opening of the valve 34 on the basis of the measurements received from the flow meter 33, to thereby control the flow rate of the propagation liquid. That is, the substrate processing apparatus 1 is configured such that the output power of ultrasonic vibrations and the flow rate of the propagation liquid can be controlled individually.

2. Operation of Substrate Processing Apparatus FIG. 4 is a flow chart illustrating the flow of a cleaning process performed by the substrate processing apparatus 1. With reference to FIG. 4, the operation of the substrate processing apparatus 1 in the cleaning process will be described below. The following operation proceeds by the control exerted by the controller 50 on the lifter drive 24, ultrasonic vibrator 40, valves 14, 34 and the like.

For cleaning a plurality of substrates W, the substrates W are first placed on the lifter 20 by a transport robot not shown. Then, the substrate processing apparatus 1 moves down the lifter 20 to immerse the plurality of substrates W in the processing liquid retained in the processing bath 10 (step S1). The lifter 20 may first be moved down, and the processing liquid may then be retained in the processing bath 10.

Next, the substrate processing apparatus 1 opens the valve 14 to supply the processing liquid into the processing bath 10 (step S2). The processing liquid is supplied from the processing liquid supply source 13 via the pipe 12 to be discharged into the processing bath 10 through the discharge ports 11. This generates a flow of the processing liquid in the processing bath 10 toward the top of the processing bath 10. At the top of the processing bath 10, the processing liquid overflows into the external bath 15.

Next, the substrate processing apparatus 1 opens the valve 34 to supply the propagation liquid into the propagation bath 30 (step S3). The propagation liquid is supplied from the propagation liquid supply source 32 into the propagation bath 30 via the pipe 31. When the propagation liquid is retained in the propagation bath 30 more than a predetermined amount so that the propagation liquid is discharged to the pipe 35, then, a flow of the propagation liquid such as shown in FIG. 3 is generated in the propagation bath 30. The substrate processing apparatus 1 continues supplying the propagation liquid until application of ultrasonic vibrations which will be discussed later is finished. When supplying the propagation liquid, the substrate processing apparatus 1 controls the valve 34 to control the amount of supply of the propagation liquid. When the amount of supply of the propagation liquid is controlled, the flow rate of the propagation liquid in the propagation bath 30 is also controlled.

Next, the substrate processing apparatus 1 operates the ultrasonic vibrator 40 to generate ultrasonic vibrations (step S4). The ultrasonic vibrations generated by the ultrasonic vibrator 40 propagate to the bottom of the propagation bath 30, the propagation liquid in the propagation bath 30, the bottom of the processing bath 10 and the processing liquid in the processing bath 10 in sequence, and reach the substrates W immersed in the processing liquid. The substrate processing apparatus 1 controls the ultrasonic vibrator 40, to thereby control the output power of ultrasonic vibrations.

Particles adhered to the substrates W are separated from the surfaces of the substrates W under the impact of the ultrasonic vibrations. Since the flow of processing liquid is generated upwardly in the processing bath 10, the particles separated from the surfaces of the substrates W are transported to the top of the processing bath 10 with the flow of the processing liquid. The particles are then transported to the external bath 15 at the top of the processing bath 10 with the processing liquid, and are discharged to the drainage line via the pipe 16.

After continuing applying the ultrasonic vibrations for a predetermined time period, the substrate processing apparatus 1 stops the operation of the ultrasonic vibrator 40 while continuing supplying the processing liquid only (step S5). Particles remaining in the processing liquid are transported to the external bath 15 with the flow of the processing liquid, and are discharged to the drainage line via the pipe 16. This prevents the particles remaining in the processing bath 10 from being adhered again to the substrates W.

Thereafter, the substrate processing apparatus 1 stops supplying the propagation liquid and processing liquid (steps S6, S7), and moves up the lifter 20 to raise the substrates W out of the processing bath 10 (step S8). The substrate processing apparatus 1 now finishes the cleaning process of the substrates W. A drying process is carried out on the substrates W with the substrates W being raised above the processing bath 10 or after the substrates W are transported to another apparatus.

In the aforementioned step S4, the flow of the propagation liquid is generated in the propagation bath 30, and ultrasonic vibrations travel in the propagation liquid. Therefore, with the resistance of the flow of the propagation liquid, the direction of travel of the ultrasonic vibrations is scattered. Particularly, since the propagation liquid flows in a direction that crosses the travel of the ultrasonic vibrations, the direction of travel of the ultrasonic vibrations is scattered effectively. This allows a concentrated impact of the ultrasonic vibrations on the substrates W to be relieved.

The controller 50 controls the output power of the ultrasonic vibrations and the flow rate of the propagation liquid individually. When increasing the output power of the ultrasonic vibrations, the controller 50 accordingly increases the flow rate of the propagation liquid. Therefore, the substrate processing apparatus 1 increases the output power of the ultrasonic vibrations to achieve an improved efficiency of particle removal as well as relieving a concentrated impact of the ultrasonic vibrations to thereby prevent a fine pattern formed on the substrates W to strip or fall down.

A user may previously determine the correlation between the output power of the ultrasonic vibrations and the flow rate of the propagation liquid by experiments or the like and may store the correlation in the controller 50. For instance, as shown in FIG. 5, the correlation may be determined such that the flow rate of the propagation liquid is low when the output power of the ultrasonic vibrations is low while the flow rate of the propagation liquid is high when the output power of the ultrasonic vibrations is high. In processing, the controller 50 may control the ultrasonic vibrator 40 and valve 34 in synchronization with each other on the basis of such correlation. Particularly when varying the output power of the ultrasonic vibrations during the processing, the controller 50 may control the flow rate of the propagation liquid on the basis of the variations in output power of the ultrasonic vibrations and the above correlation.

A user may previously determine the output power of ultrasonic vibrations and the flow rate of the propagation liquid to be used according to the type of substrates W to be processed or the type of processing (a so-called processing recipe).

The substrate processing apparatus 1 can minutely control the impact of ultrasonic vibrations by controlling the flow rate of the propagation liquid. The substrate processing apparatus 1 can thereby correct minor differences inevitably occurring in ultrasonic vibrations from another substrate processing apparatus 1.

3. Modification

One preferred embodiment of the present invention has been described above, however, the present invention is not limited to the above description. For instance, the supply of the processing liquid may be stopped when operating the ultrasonic vibrator 40 in step S4.

Further, the substrate processing apparatus 1 may include a sensor for detecting the impact of ultrasonic vibrations in the processing bath 10, and may be configured such that the detection by the sensor is received at the controller 50. With such configuration, the controller 50 can control the valve 34 on the basis of the detection received from the sensor. The substrate processing apparatus 1 can thereby control the flow rate of the propagation liquid on the basis of measured values of output power of ultrasonic vibrations.

In the aforementioned substrate processing apparatus 1, the pipe 16 is connected to the drainage line, but may be connected to the pipe 12. With such configuration, the processing liquid overflown to the external bath 15 is supplied again into the processing bath 10. This reduces the consumption of processing liquid.

Further, in the aforementioned substrate processing apparatus 1, the pipe 35 is connected to the drainage line, but may be connected to the pipe 31. With such configuration, the propagation liquid discharged from the propagation bath 30 is supplied again into the propagation bath 30. This reduces the consumption of propagation liquid.

Furthermore, the aforementioned substrate processing apparatus 1 is intended to perform cleaning of substrates, but may perform other processing such as etching.

4. Examples

FIG. 6 is a diagram illustrating experimental results (for comparison) of the number of defects occurred per substrate W immersed in the processing liquid in the processing bath 10 while operating the ultrasonic vibrator 40 for a predetermined time period in the substrate processing apparatus 1 of the above configuration with the propagation liquid in the propagation bath 30 being kept still (that is, with the flow of propagation liquid being stopped). The horizontal axis of the diagram of FIG. 6 indicates the output power of ultrasonic vibrations generated by the ultrasonic vibrator 40, and the vertical axis indicates the number of defects occurring per substrate W. In the experiments shown in FIG. 6, the frequency of ultrasonic vibrations was set at 1000 Hz, and deionized water was used for the propagation liquid and processing liquid. Further, a 200-mm diameter test semiconductor wafer with a 90-nm generation gate pattern formed thereon was used for substrates W to be processed. The results shown in FIG. 6 have revealed that the number of defects occurred per substrate W increases along with the increase in output power of ultrasonic vibrations.

FIG. 7 is a diagram illustrating repeated experimental results (for comparison) of the number of defects occurred per substrate W under the same conditions as in the experiments shown in FIG. 6 to obtain variations and an average value in each of the cases where the output power of ultrasonic vibrations was 100W and where it was 200W. The results shown in FIG. 7 have revealed that about 0 to 120 defects occurred per substrate W when the output power of ultrasonic vibrations was 100W, while about 5 to 110 defects occurred per substrate W when the output power of ultrasonic vibrations was 200W.

FIG. 8 is a diagram illustrating experimental results of the sound pressure of ultrasonic vibrations propagated in the processing liquid in the processing bath 10 while operating the ultrasonic vibrator 40 with the flow of propagation liquid being generated in the propagation bath 30 in the substrate processing apparatus 1 of the above configuration. The horizontal axis of the diagram of FIG. 8 indicates the flow rate of propagation liquid in the propagation bath 30, and the vertical axis indicates sound pressure values of ultrasonic vibrations measured in the processing liquid in the processing bath 10. In the experiments shown in FIG. 8, the output power and frequency of ultrasonic vibrations generated by the ultrasonic vibrator 40 were set at 500W and 1000 Hz, respectively, and deionized water was used for the propagation liquid and processing liquid. The results shown in FIG. 8 have revealed that sound pressure values of ultrasonic vibrations in the processing bath 10 decrease with increasing the flow rate of the propagation liquid, and increase with decreasing the flow rate of the propagation liquid. That is, it shows that the sound pressure of ultrasonic vibrations can be controlled by controlling the flow rate of the propagation liquid.

FIG. 9 is a diagram illustrating repeated experimental results of the number of defects occurred per substrate W immersed in the processing liquid in the processing bath 10 while operating the ultrasonic vibrator 40 for a predetermined time period with the flow of propagation liquid being generated in the propagation bath 30 at 3.8 L/min in the substrate processing apparatus 1 of the above configuration to obtain variations and an average value in each of the cases where the output power of ultrasonic vibrations was 100W and where it was 200W. The horizontal axis of the diagram of FIG. 9 indicates the output power of ultrasonic vibrations generated by the ultrasonic vibrator 40, and the vertical axis indicates the number of defects occurred per substrate W. In the experiments shown in FIG. 9, the frequency of ultrasonic vibrations was set at 1000 Hz, and deionized water was used for the propagation liquid and processing liquid. Further, a 200-mm diameter test semiconductor wafer with a 90-nm generation gate pattern formed thereon was used for substrates W to be processed. The results shown in FIG. 9 have revealed that the number of defects occurred per substrate W was zero either when the output power of ultrasonic vibrations was set at 100 W or 200 W. Comparison between the results shown in FIGS. 7 and 9 shows that the number of defects occurred per substrate W was significantly reduced by generating the flow of the propagation liquid in the propagation bath 30.

The above experiments show that controlling the flow rate of the propagation liquid in the propagation bath 30 allows control of sound pressure values of ultrasonic vibrations that act upon substrates W immersed in the processing liquid in the processing bath 10, which hence allows reduction of the number of defects occurring on the substrates W. In the above examples, the frequency of ultrasonic vibrations was set at 1000 Hz, however, it is considered that similar effects can be obtained in any other frequency band. It is considered that effects similar to those of the present invention can sufficiently be obtained even when the frequency of ultrasonic vibrations is set at 700 to 2000 Hz, for example.

While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention. 

1. A substrate processing apparatus for immersing a substrate in a processing liquid to process said substrate, said substrate processing apparatus comprising: a processing bath retaining said processing liquid; a holder holding said substrate in said processing bath; an ultrasonic vibration generator generating ultrasonic vibrations; a propagation bath retaining a propagation liquid for propagating said ultrasonic vibrations generated by said ultrasonic vibration generator to said processing bath; a liquid flow generator generating a flow of said propagation liquid in said propagation bath; and a flow rate controller controlling a flow rate of said propagation liquid generated by said liquid flow generator.
 2. The substrate processing apparatus according to claim 1, wherein the flow of said propagation liquid is generated in a direction that crosses travel of said ultrasonic vibrations in said propagation bath.
 3. The substrate processing apparatus according to claim 2, wherein said ultrasonic vibration generator is capable of controlling an output power of said ultrasonic vibrations, said substrate processing apparatus further comprising a controller controlling said ultrasonic vibration generator and said flow rate controller in synchronization with each other.
 4. The substrate processing apparatus according to claim 3, wherein said liquid flow generator includes a supplier supplying said propagation liquid into said propagation bath and a discharger discharging said propagation liquid from said propagation bath.
 5. The substrate processing apparatus according to claim 4, further comprising a flow meter measuring the amount of supply of said propagation liquid by said supplier, wherein said flow rate controller controls the flow rate of said propagation liquid on the basis of measurement by said flow meter.
 6. The substrate processing apparatus according to claim 5, wherein said processing bath has its bottom immersed in said propagation liquid retained in said propagation bath, and said ultrasonic vibration generator generates said ultrasonic vibrations from the bottom of said propagation bath toward the bottom of said processing bath.
 7. The substrate processing apparatus according to claim 6, wherein said supplier and said discharger are provided in opposite sides to each other with said processing bath interposed therebetween.
 8. The substrate processing apparatus according to claim 7, wherein said controller controls said ultrasonic vibration generator and said flow rate controller in synchronization with each other on the basis of a predetermined correlation.
 9. The substrate processing apparatus according to claim 8, wherein said propagation liquid is deionized water.
 10. A substrate processing method of processing a substrate, comprising the steps of: (a) immersing a substrate in a processing liquid retained in a processing bath; (b) generating ultrasonic vibrations; (c) propagating said ultrasonic vibrations to said processing bath through a propagation liquid; (d) generating a flow of said propagation liquid; and (e) controlling a flow rate of said propagation liquid.
 11. The substrate processing method according to claim 10, wherein in said step (d), the flow of said propagation liquid is generated in a direction that crosses travel of said ultrasonic vibrations.
 12. The substrate processing method according to claim 11, further comprising the step of (f) controlling an output power of said ultrasonic vibrations.
 13. The substrate processing method according to claim 12, wherein in said step (e), the flow rate of said propagation liquid is controlled on the basis of the output power of ultrasonic vibrations controlled in said step (f).
 14. The substrate processing method according to claim 13, wherein said propagation liquid is retained in a propagation bath, and in said step (d), the flow of said propagation liquid is generated by supply of said propagation liquid into said propagation bath and discharge of said propagation liquid from said propagation bath. 